This invention relates generally to digital advanced television (ATV) transmission systems (i.e., digital high definition television (HDTV) and digital standard definition television, and particularly to ATV terrestrial transmission systems which are exposed to interference from ATV or NTSC signals operating on the same channel assignment. The ATV signal comprises a VSB (vestigial sideband) type transmission having data frames that are organized into repetitive data segments of 832 multilevel symbols each. Each data frame has a first data field sync segment followed by 312 data segments and a second data field sync segment followed by another 312 data segments. Each data segment consists of a four symbol segment sync followed by 828 data and forward error correction (FEC) symbols.
The ATV signal may be transmitted on current NTSC channels including so-called "taboo" or unusable NTSC channels. A high data rate cable mode supports two or more, depending upon their resolution, ATV signals in one 6 MHz channel, whereas a lower data rate, but more robust, terrestrial mode supports one or more, depending upon their resolution, ATV signals in one 6 MHz channel with minimum interference to or from NTSC signals.
The ATV system, when transmitting signals in the presence of NTSC co-channels, includes ATV receivers that are constructed and arranged to minimize the interference from the NTSC co-channels. In general, an NTSC rejection filter may be used in the ATV receiver for providing a high rejection rate at the NTSC signal visual, color and audio carriers. The transmitted ATV signal, which includes a small pilot coincident with a suppressed carrier near the lower edge of the channel in accordance with the invention, is positioned relative to the NTSC visual carrier to enhance the operation of the NTSC rejection filter in the case of NTSC co-channel signals and to minimize interference from a nearby co-channel ATV signal where that condition obtains.